1. Field of the Invention
The present invention relates to a flexible tube to be used in a sprinkler system for fire suppression, which is installed in the ceiling of building, and more particularly, to a structure and a method for coupling a meshed protective net made of stainless steel to a flexible tube, in which when high pressure is applied to the flexible tube used as a high pressure piping in a sprinkler system, expansion and subsequent deformation or bursting of the flexible tube are prevented.
2. Description of the Related Art
Conventionally, a sprinkler system is installed in the ceiling of a building, as shown in FIG. 1. A top panel (A) is attached to the lower side of the sprinkler system. A support member 3 is fixed on a top bar 2 with the aid of a locking member 1. A reducer 4, in the lower end of which a sprinkling head 5 is fitted, is fixed in the support member 3 with the aid of a locking member 6. One end of the reducer 4 is connected to a flexible tube 7 by a method such as welding. The other end of the flexible tube 7 is connected to a main tube (not shown) and a nipple 9, feeding the sprinkling head 5 with extinguishing fluid.
A flexible tube for a sprinkler must be installed not to overlap a heating and cooling duct, a top joist, an electrical communication tube, an electric lamp, and the like, in a small ceiling space. For this purpose, the flexible tube must have a high flexibility not to burst even upon bending several times. In addition, even in the case where high pressure extinguishing fluid of more than 17.5 kg/cm2 is provided, in order for the sprinkling head not to separate from the top panel, a flexible tube, in which the degree of expansion is small, must be used. However, generally, when a flexible tube with crest and valley portions is provided with high pressure extinguishing fluid, it is undesirably expanded to deform or crack, thereby bursting. To prevent these phenomena, flexible tube is conventionally reinforced by coupling a meshed protective net made of steel wire thereto.
A method is reported in which a flexible tube is coupled with a protective net, as shown in FIG. 2. Stopper projections 11 are formed on straight tube portions of both ends of the flexible tube 10 with crest and valley portions. Then, inner locking rings 31 are fitted around the straight tube portions 12 adjacent to both ends of the stopper projections 11. Then, the flexible tube 10 is wrapped with a meshed cylindrical protective net made of steel wire, in a manner such that both ends 21 of the protective net 20 encircle the inner locking rings 31. Then, outer locking rings 32 are fitted thereon. Then, when the outer locking rings 32 so formed are compressed and fastened inwardly, each of ends 21 of the protective net is fastened between the inner and outer locking rings 31, 32, with the result that the protective net 20 is coupled to the flexible tube 10.
However, in the above method, in which the flexible tube 10 and protective net 20 are coupled, potentiometric corrosion and crevice corrosion occur between the flexible tube 10 or protective net 20, each made of austenite stainless steel, and the inner or outer locking rings 31, 32, each made of iron, with the result that fatal defects are created in the flexible tube. Specifically, crevice corrosion and potentiometric corrosion occurring between different metals are found in the gap 33 defined between the inner locking ring 31 and the straight tube portion 12 of the flexible tube. This causes fatal defects such as perforation or cracking in the straight tube portion 12 of the flexible tube in the form of thin plate tube of 0.3 mm-0.4 mm in thickness. Each of ends of the protective net 21 placed in the gaps 34 between the inner and outer locking rings 31, 32, is corroded, whereby the protective net 20 is easily separated from the flexible tube 10.
In addition, in the course of fastening the outer locking ring 32 to the inner locking ring 31 in order to fasten the end 21 of the protective net between the inner and outer locking rings 31, 32, the straight tube portion 12 of the flexible tube is subjected to pressure to be deformed or stressed. The above method for coupling the protective net 20 to the flexible tube 10 involves forming the stopper projections 11 in both ends of the flexible tube, fitting the inner and outer locking rings 31, 32 around the straight tube portions 12, and compressing the outer locking rings 32. As a result, there are problems in that the working process is complicated and the number of parts increases, thereby the unit cost of production is high.
Meanwhile, as shown in FIG. 3, another prior art concerns a method for coupling a protective net to a flexible tube, comprising wrapping a flexible tube 10′ with a protective net 20′, fitting a weld ring 30′ around the end of the protective net 20′, and welding the end of the flexible tube 10′, the end of the protective net 20′, and the end of the weld ring 30′.
In the above method, however, in the course of forming crest and valley portions in the flexible tube 10′, stress and work hardening inevitably occur. Generally, in order to remove the stress and work hardening, the flexible tube is solution heated at a temperature of 1,050° C. to 1,150° C., followed by welding. During the welding process, carbides are undesirably precipitated and thus intergranular corrosion occurs in portions heated at a temperature of 450° C. to 850° C., a brittleness temperature of a stainless steel, by welding heat of 1,400° C. to 1,500° C. This may cause fatal defects in thin plate flexible tubes. Furthermore, crevice corrosion occurs in gap 33′ defined between the weld ring 30′ and the flexible tube 10′. Still furthermore, the weld ring 30′ is separately required, and a welding process must be separately carried out after solution heating the flexible tube 10′ in order to remove stress generated during shaping the flexible tube 10′. As a result, the production process is complicated and the unit cost of production is high.